The present invention relates to a a process for determining a run-away condition of a rotation-speed controlled, permanent-excited synchronous motor and to a device for carrying out the process.
Rotation-speed controlled, permanent-excited synchronous motors are commercially available. Certain procedures are implemented that can be used to identify the correct pole position of the permanent-excited pole rotor for commutating the synchronous motor. All these procedures are relatively reliable and accurate. However, commutation errors can occasionally occur which can cause the rotation-speed controlled, permanent-excited synchronous motor to run away. Synchronous motors in that run away can damage or destroy a production machine or machine-tool in which the synchronous motor is installed.
Although commutation errors occur very rarely, they have to be prevented at all cost because of the potential for consequential damages. A commutation error can have many causes which depend on the components which cooperate with the drive. It is therefore not sufficient to merely analyze the errors that have occurred in the past.
To this date, the rotation speed controller of the rotation-speed controlled, permanent-excited synchronous motor is monitored to determine if the rotation speed controller has reached a limit setting. It can be safely assumed that a fault has occurred when a maximum or minimal controlling variable is generated at the output of the rotation speed controller during a predetermined time interval. The predetermined time interval is typically preset at the factory to, for example, approximately 100 msec, and the length of this time interval can be increased by a user. However, it is impossible to determine from the error signal the reason why the rotation speed controller has reached the limit setting. There can be numerous reasons why the rotation speed controller has reached the limit setting. Of these reasons, only one represents a commutation error that can cause the rotation-speed controlled, permanent-excited synchronous motor to run away.
A commutation error may already have accelerated a load to a high speed after the expiration of the predetermined time period, depending on the inertial mass of a connected load. If an error message is generated, a converter connected to the rotation-speed controlled, permanent-excited synchronous motor is switched off by a conventional pulse blocking device. Depending on the existing friction, the load then coasts to a stop. If the load was already accelerated to a high speed during the predetermined time period, then the pulse blocking device can no longer prevent a crash. For this reason, production machines and machine tools are protected by a limiter in form of a buffer that intercepts a load that coasts to a stop.
It would therefore be desirable and advantageous to provide an improved process and device for determining a run-away condition of a rotation-speed controlled, permanent-excited synchronous motor, which obviates prior art shortcomings and is able to specifically bring the motor and an associated drive to a safe stop.